GB2220993A

GB2220993A - Sliding bearing

Info

Publication number: GB2220993A
Application number: GB8912734A
Authority: GB
Inventors: Sanae Mori; Masaaki Sakamoto; Hideo Ishikawa; Yoji Nagai
Original assignee: Daido Metal Co Ltd
Current assignee: Daido Metal Co Ltd
Priority date: 1988-06-02
Filing date: 1989-06-02
Publication date: 1990-01-24
Anticipated expiration: 2009-06-02
Also published as: KR920006923B1; DE3917694A1; KR900000608A; JPH01307512A; US5116692A; DE3917694C2; GB8912734D0; GB2220993B; JPH0814287B2

Description

1 MULTI-LAYER BEARINGS 2 2 r12 0 9 9 3.

The present invention relates to bearings suitable for use in automobiles, ships, agricultural machines and the like and, more particularly, to a multi-layer type sliding bearing of aluminium alloy which excels in the anti-seizure property, the anti-fatigue property and the anti-fretting property.

to It has heretofore been common practice that sliding bearings of aluminium alloy are used in gasoline engines or engines for small automobiles with the sliding-bearing surface being coatedwith no overlay. On the other and, bearings of aluminium fc-; alloy which have an Ni-plating intermediate layer and an overlay consisting essentially of a Pb alloy have been employed in the field of sliding bearings which are primarily used with special types of engines such as high-load engines or medium-speed diesel engines. Another example of the prior art is known in which Sn or an Sn alloy is applied as an overlay to a bearing of Cu-Pb alloy or Pb-bronze alloy which is exclusively intended for engines for use in specific types of medium-or low-speed ship. This prior art makes use of the properties of Sn alloys having corrosion resistance and abrasion resistance which are high compared to those of Pb alloys. The art of providing an Sn overlay on an aluminium alloy is shown in Japanese Patent Unexamined Publication No 61- 153286, which discloses a bearing member in which a bearing layer of aluminium alloy is directly plated with Sn without an Ni intermediate layer.

The opportunities for employing gasoline engines 2 or diesel engines for use in small automobiles such as passenger cars in the range of high-speed rotation have been increasing particularly recently. In the situation, it has been desired to improve to a great extent the seizure resistance, abrasion resistance, fatigue resistance, corrosion resistance and fretting resistance of engine bearings.

As is known, a conventional type of bearing of CuPb or Pb-bronze alloy provided with an Pb-alloy overlay 10 is disadvantageous in terms of corrosion resistance. Moreover, it has recently been noted that the properties of lubricating oils deteriorate rapidly and seriously during use, particularly due to an extension in the life of engine be arings and a rise in oil It; temperature as a result of an increase in the rotational speed of engines. In particular, an organic acid resulting from the deterioration of lubricating oil is apt to corrode the Cu-Pb alloy or the Cu-bronze alloy to a remarkable extent. In addition, in order to achieve a reduction in the manufacturing cost of 2f) J11 engines, there are many cases where crankshafts are made of ductile cast iron. However, the use of ductile cast iron often causes rapid abrasion or rapid seizure in the above-described conventional three-layer type bearings.

In view of the problems, bearings of aluminium alloy have recently been employed in place of such CuPb type three-layer bearings. Aluminium alloys are generally compatible in nature with shafts of ductile iron and have a satisfactory corrosion-resistant property. However, if a bearing made of such an aluminium alloy is employed without an overlay, partial striking or misalignment is apt to occur. Moreover, 1 3 since dust is not easily separated from aluminium alloys, the phenomenon of seizure may take place early in the service life of the bearing if the application conditions are not satisfactory. If an overlay consisting essentially of a conventional Cu alloy is provided on such a bearing of aluminium alloy as shown in Japanese Patent Unexamined Publication No 62- 110021, it follows that the problems of corrosion resistance and abrasion resistance are again encountered. To overcome these problems, Japanese Patent Unexamined Publication No 60-36641 discloses the art of utilising, instead of an Pb alloy, an Sn alloy as an overlay. Japanese Patent Unexamined No 61-153286 discloses a bearing member in which. a bearing layer of aluminium jr, alloy is directly plated with Sn without an Ni intermediate layer.

These conventional methods utilising overlays, however, have the following problems. In a case where an overlay is provided on an aluminium alloy by electroplating, it is customary to provide an intermediate layer of Ni, Co, Fe or the like in order to ensure the adhesion of the overlay. However, such an intermediate layer is extremely hard and, when the overlay wears out so that the surface of the intermediate layer is exposed, the intermediate layer comes into frictional contact with the shaft to cause seizure or galling. Various disadvantages incurred by the provision of the intermediate layerhave been pointed out, particularly in recent years. Although there exists a method of directly providing an overlay without forming the intermediate layer, the bonding strength of the overlay which is realised by this method is extremely low compared to the bonding 1 !J 4 strength of an overlay combined with an intermediate layer (in the prior art, typically having 0.5 to 3.0 pm in thickness). This type of overlay which is directly provided has a good initial compatibility but inferior durability and there is such disadvantage that laminar abrasion or the exfoliation of the overlay is apt to occur. For this reason, this overlay has been merely provided as a sacrificing layer.

Moreover, the recent trend toward reductions in 11) the size and weight of engines has lead to decrease in rigidity of the housing of an engine, so that the phenomenon of fretting (the phenomenon of abrasion occurring between two contacting surfaces which are exposed to a relative mdtion of small amplitude) occurring on the rear face of the bearing has become a serious problem to be improved.

It is, therefore, a first object of the present invention to provide a multi-layer type sliding bearing of aluminium alloy in which the disadvantages of the prior art are reduced as well as to provide a method of -producing the same.

It is a second object of the present invention to provide a multi-layer type sliding bearing of aluminium alloy in which the disadvantages of the prior art are reduced and on the rear face of which fretting is

1 minimised as well as to provide a method of producing the same.

To achieve the first object, in accordance with a first -aspect of the present invention, there is provided a multi-layer type sliding bearing of aluminium alloy which has a backing layer of steel, a bearing layer of aluminium alloy bonded to the backing layer, an overlay and a mixture layer of a thickness of not more than 0.5pm between the bearing layer and the overlay in a bonded relation to both the bearing layer and the overlay, the mixture layer being constituted by the mixture of the overlay and one element selected from the group consisting of Ni, Co and Fe, the overlay consisting by weight of 0 to 15% Cu, 0 to 20% Sb, and the balance Sn and incidental impurities.

To achieve the second object, the backing layer preferably has, bonded to its side opposite to that of the bearing layer, a rear face-plating layer. Preferably, the face-plating layer consists of the same constituents as the overlay and has a thickness in a range of 0.1 to 5 pm. If the thickness is smaller than 0.1 pm, it is impossibleto obtain the effect of preventing fretting even if the rear face-plating layer is provided, while if the thickness is greater that 5 )-,m, the phenomenon of migration is apt to occur (that is, a phenomenon in which foreign matter, degraded matter, or powder due to abrasion are collected and accumulated between two contacting surfaces due to small relative motions).

The thickness of the mixture layer is preferably 0.05 to 0.3 microns.

2,71 The overlay preferably consists by weight of not more than 5% Cu, 0.5 to 10% Sb, and the balance Sn.

A method of producing a multi-layer type sliding bearing of aluminium alloy comprises, according to a second aspect of the present invention, providing a half cylindrical or cylindrical bearing member made of an aluminium alloy, the bearing member being bonded JO onto a backing layer of steel, electrolytically providing an overlay on the inner face of the bearing member which overlay consists by weight of 0 to 15% Cu, 6 0 to 20% Sb, and the balance Sn and incidental impurities, and providing a mixture layer having a thickness of not more than 5 pm between the overlay and the bearing layer of aluminium alloy by a combination of an electroless substitution method and an overlay electroplating method, the mixture layer being constituted by a mixture of the constituents of the overlay and one element selected from the group consisting of Ni, Co and Fe.

lo The present inventors found that if a mixture layer which has a thickness of not more than 0.5 pm and which is constituted by a mixture of the constituents of the overlay and one element selected from the group consisting of Ni, Co andFe is provided between the jr, bearing layer of aluminium alloy and the overlay of a multi-layer type sliding bearing, it is possible to reduce all of the aforesaid disadvantages of the prior art, that is, the disadvantage experienced with bearings of aluminium alloy without overlays, the

21) disadvantage involved in the art of providing an overlay without an intermediate layer, and the disadvantage involved in the art of providing an overlay with an intermediate layer. Briefly the mixture layer having a thickness of not more than 0.5 pm serves to enhance the bonding strength between the overlay and the bearing layer of aluminium alloy, thereby preventing the laminar abrasion or the exfoliation of the overlay. In addition, even after the overlay has been lost due to abrasion, it is possible to completely prevent galling between the shaft and the bearing.

If the thickness of the mixture layer is more than 0.5 pm then, when the overlay has been lost due to 7 abrasion, the bearing and the shaft are apt to suffer seizure and galling.

Cu and Sb have the effect of enhancing the durability of the overlay without deteriorating the compatibility inherent in Sn which is a primary component of the overlay. However, if the Cu content exceeds 10% and/or if the Sb content exceeds 20%, the overlay-forming alloy becomes brittle and fatigue cracks easily occur due to impact loads. Moreover, the 11) hardness of this overlay-forming alloy increases to lower the compatibility necessary in the overlay.

Further, according to a preferred feature, it is possible to suppress the occurrence of fretting by providing on the surface'of the backing layer which i located on the rear side of the bearing a plating layer which consists of the same constituents as those of the overlay provided on the inner face of the bearing layer. The thickness of this plating layer provided on the rear face of the bearing is 0.1 to 5 um, preferably 211 0.5 to 5 um. If this thickness is smaller than O.Ipni, the effect of the plating layer will become small and the rust preventing effect on the backing layer is therefore reduced. on the other hand, if the thickness is greater than 5)1m, the aforesaid migration is apt to occur and the performance of the bearing is therefore reduced. Moreover, variations may occur in the thickness of the plating layer during production thereof. For these reasons, a thickness greater than 5 pm is not desirable. For the sake of simplification of the production process, it is preferably to provide this plating layer on the surface of the backing layer, which is located on the rear-face side of the bearing, by electroplating at the same time as the overlay is 1 t; 8 provided on the inner surface of the bearing layer which is located on the inner side of the bearing. However, it is possible to provide a rear face-plating layer which consists of constituents which differ from those of the overlay, and it is also possible to add the rear face-plating layer in a process step separate from the process step of providing the overlay.

In the case of bearings for use in applications which require no antifretting property, it is not necessary to provide the platting layer on the surface of the backing layer which is located on the rear sidc, of the bearing.

The invention may be carried into practice in various ways but, by wa of example, two bearings embodying the invention and two prior art bearings to provide comparison will now be described with reference to the accompanying drawings in which:

2 t; 1 (1 Fig 1 is a schematic view of the sectional 21) structure of a sliding bearing. according to a first embodiment of the present invention; Fig 2a is a schematic view of the sectional microstructure of a conventional sliding bearing having an overlay provided with an intermediate layer; Fig 2a-1 is a schematic view showing the surface analysis of the intermediate layer of Fig 2a using an electron probe microanalyzer (hereinafter referred to as 11EMPA11); Fig 2b is a schematic view of the sectional microstructure of a conventional sliding bearing having an overlay without an intermediate layer; Fig 2b-1 is a schematic view showing the surface analysis, using EPMA, of each layer shown in Fig 2a; 9 h) Fig 2c is a schematic view of the sectional microstructure of the sliding bearing shown in Fig 1 embodying the present invention; Fig 2c-1 is a schematic view showing the surface analysis, using EPMA, of the mixture layer shown in Fig 2c; and Fig 3 is a schematic view of the sectional structure of a sliding bearing according to a second embodiment of the present invention.

Fig 1 shows a first embodiment of a multi-layer type sliding bearing of aluminium alloy. The illustrated multi-layer type sliding bearing of aluminium alloy has an overlay 1, a mixture layer 3, a bearing layer 4 of aluminium alloy, and a backing layer 5 of steel. The overlay 1 is bonded to one side of the bearing layer 4 of aluminium alloy with the mixture layer 3 interposed therebetween, and the other side of the bearing layer 4 of aluminium alloy is 211 bonded to the backing layer 5. The overlay 1 substantially consists by weight of 0 to 15% Cu, 0 to 20% Sb, and the balance Sn and incidental impurities. The mixture layer 3, which has a thickness of not more than 0. 5 pm (microns), is formed between the overlay 1 21; and the bearing layer 4 of aluminium alloy in such a manner that the mixture layer 3 is bonded to both the overlay 1 and the bearing layer 4. The mixture layer 3 is constituted by a mixture of the constituents of the overlay 1 and one element selected from the group consisting of Ni, Co and Fe.

Fig 3 shows a second embodiment of the multilayer type sliding bearing of aluminium alloy according to the present invention. The illustrated multilayer I-T r? type sliding bearing of aluminium alloy has a rear face plating layer 6 in addition to the overlay 1, mixture layer 3, the bearing layer 4 of aluminium alloy, andthe backing layer 5 of steel which are shown , in Fig 1. The bearing layer 4 of aluminium alloy is bonded to the inner face (upper side as viewed in Fig 3) of the backing layer 5, and the overlay 1 is bonded to the bearing layer 4 of aluminium alloy with the. mixture layer 3 interposed therebetween in a manner lql similar to that shown in Fig 1. The rear face-plating layer 6 is bonded to the outer face (lower side as viewed in Fig 3 of the backing layer 6 of steel and consists of constituents which are the same as those of the overlay 1. The ove.lay 1 substantially consists by Is weight of 0 to 15% Cu, 0 to 20% Sb, and the balance Sn and incidental impurities. The mixture layer 3, which has a thickness of not more than 0. 5 microns, is formed between the bearing layer 4 of aluminium alloy and the overlay 1 in such a manner that the mixture layer 3 is 21) bonded to both the overlay 1 and the bearing layer 4. The mixture layer 3 is constituted by a mixture of the constituents of the overlay and one element selected from the group consisting of Ni, Co and Fe, and the rear face-plating layer 6 preferably has a thickness of 0.1 to 5 microns.

The first and second embodiments will be explained in more detail below with reference to examples thereof.

To prepare a metal sheet for a bearing layer of aluminium alloy, an aluminium-alloy sheet which consisted by weight of 12% Sn, 2.5% Si, 1.7% Pb, 1% Cu, 0.3% Sb, and the balance A1 was pressure-bonded, by rolling, to a backing metal of steel having a thickness the 11 of 1.20 mm and the same configuration as that of the aluminium-alloy sheet. Then, this metal sheet was treated by heating at 3500C for four hours to produce a bimetal strip (1.65 mm in thickness and 110 inm in width) as a material for sliding bearing. This bimetal strip was press- formed into a half cylindrical bearing member of size suitable for bearing performance tests, then mechanically worked into a predetermined size (56 mm in an outer diameter, 17 mm in length and 1.5 mm in thickness), and then degreased with a solvent. Thereafter, the bearing member was subjected to alkali etching in an aqueous solution of anhydrous sodium carbonate, sodium phosphate, and sodium hydroxide at a temperature of 500C for about 60 seconds, The alkalietched bearing member was next subjected to acid treatment, followed by zincate treatment (the treatment of dissolving zinc oxde in an aqueous solution comprising essentially sodium hydroxide, immersing the bearing member in this aqueous solution at 200C for about 20 seconds, and precipitating zinc on the surface of the bearing member). The thus treated bearing member was then subjected to electroless plating with Ni (whose liquid concentration was adjusted so that a plating layer having a thickness of 0.05 to 0.2 microns could be formed by immersing the bearing member in an aqueous solution essentially comprising nickel sulphate, at 500 for about 15 to 60 seconds, preferably for 30 seconds). The thus-treated metal was finally subjected to electroplating for providing an overlay and electroplating for providing a rear face-plating layer at the same time. In each of these electroplating steps, the liquid concentration and the magnitude of electric current were determined so that a 1 r 1 1 12 plating layer having a thickness of about 0.8 microns could be formed by energization of about 60 seconds. In this manner, a finished bearing product was prepared. In each finished bearing product.according to this embodiment,the inner-face overlay was 8 microns thick, the Ni-overlay mixture layer 0.1 microns thick, the bearing layer of aluminium alloy 0.3 mm thick, the backing layer of steel 1.2 mm, and the rear face-plating layer 1.5 micron thick.

lo In order to compare this finished bearing product of the embodiment with conventional products, the materials, size and process which were the same as those used in the above embodiment were utilised to produce three kinds of domparative products according Is to the prior art. one kind was a bearing with no overlay, another kind being a bearing including an overlay which was directly provided on a bearing layer of aluminium alloy, and the other kind is a bearing including an Ni intermediate layer (2 microns thi.c-,)

117 provided on a bearing layer of aluminium alloy and an overlay provided on this intermediate layer. Moreover, the Sb content and the Cu content in the Snbase alloy which constituted the overlay were varied to investigate the resultant variations in the properties of the overlay of the above bearing of this embodiment. Further, in order to confirm the improved effect of improving the fretting, a bearing was produced which was the same as the above-described finished bearing product of the embodiment except that the thickness of the rear face-plating layer of 8 microns in thickness was provided, and this bearing was subjected to a comparative test.

Table 1 shows the bonding strength between an overlay and a bearing of aluminium alloy, maximum fatigu- load, and maximum seizure load which w-robtaiti,--r-1 through t-sts conducted with bearing sampl-s.

TABLE 1

Overlay Bonding Bonding Maximum Maximum constituents layer strength fatigue load seizure load (kgf/cm2) (kgf/cm2) Sn Mixture layer Sufficient 900 1200 Products Sn-MSb Mixture layer Sufficient 950 1200 of the present Sn-5% Cu Mixture layer Sufficient 950 1200 invention Sn-2%Cu-6%Sb Mixture layer Sufficient 950 1200 No overlay 700 1000 Sn No layer Exfoliated 500 900 with tape (Exfoliated) (Exfoliated) Products 2-micron thick for Sn intermediate Sufficient 850 950 comparison Ni layer (Seized) Sn-25%Sb Mixture layer Sufficient 950 1000 Sn-20Ub Mixture layer Sufficient 950 1000 W 14 2 t; 11) In Table 1, the maximum fatigue load is the maximum load within which no fatigue occurred as the result of a 20-hour continuous running with a rotational speed of 3,250 r.p.m. when a lubricating oil of SAE 20, preheated at 1000C, was used. The maximum seizure load is decided in such manner that, after effecting a 1-hour continuous no-load accustomed running at a rotational speed of 3,600 r.p.m. with a I" lubricating oil of SAE 20 preheated at 1000C, the level of loading was cumulatively increased by 50 kgf/cm2 each time ten minutes elapsed, and the seizure was assumed to occur when the temperature of the rear face of the bearing exceeded '2200C or when the value of electric current for driving the shaft during the test exceeded 20 amperes.

Regarding the bonding strength of the overlay with respect to the bearing layer of aluminium alloy, as can be seen from Table 1, the overlay, which was directly 211 provided on the bearing layer..of aluminium alloy without the use of a bonding layer, was easily exfoliated in an exfoliation test using an adhesive tape. In either case of the bearing of this embodiment which had a mixture layer and the prior art bearing having the 2-micron thick Ni intermediate layer, the overlay exhibited a sufficient bonding strength.

The maximum fatigue loading of each bearing sample was as follows. The maximum fatigue loadings of the bearing with no overlay and the bearing having an overlay of inferior bonding strength were small values. The bearing having the 2-micron thick intermediate layer of Ni caused seizure before reaching its maximum fatigue loading. In the case of this bearing, Ni was exposed due to the partial abrasion of the overlay and it is considered, therefore, that the. seizure was caused by the Ni-exposed portion. The bearings eacii having a mixture layer consisting of a mixture of NI and an overlay showed a sufficiently high level of maximum fatigue load whether they were products of this invention or comparative products.

The maximum seizure load of each bearing sample was as follows. The, maximum seizure load of the bearing with no overlay was a small value. In the case of the bearing having an overlay directly provided on a bearing layer of aluminium alloy, the temperature of the rear face of the bearing exceeded 2200C when the load was increased to 9SC kgf/CM2 and, at this time, the overlay of the bearing caused exfoliation. The bearing having the 2-micron thick Ni intermediate layer caused seizure at the time when its load reached 950 kgf/cm2, in which case the exposure of the Niplating layer was observed on the surface of the bearing. Tlie maximum seizure load of the bearings each having a mixture layer consisting of a mixture of Ni and an overlay was a relatively small value when the Sb content and the Cu content were large. It is considered that this resulted from the fact that the hardness of the overlay excessively increased by the high level of Sb or Cu to thereby reduce the compatibility of the overlay.

Next, other bearings were produced utilising the same production conditions and materials as those used in the above embodiment shown in Table 1 except that AI - 17%Sn - 1.7%Pb 0.9%Cu - 0.3%Sb (AlSn type alloy), Al - MPb 5%Sn 4%Si - 1%Cu (A1-Zn type alloy), and A1 - 3.5%Zn 30-Si 1%Pb 1%Cu (A1-Zn type alloy) 21) -1 1; 16 1 r, 2 r; were employed for the respective bearing layers of aluminium alloy. These bearings were also subjected to the tests which were the same as those explained in connection with Table 1. In this case, the results also showed tendencies similar to those of the results shown in Table 1.

Next, still other bearings were produced utilising the same production conditions and materials as those used in the above embodiment shown in Table 1 except H1 that their respective mixture layers were a mixture layer consisting of Co and overlay and a mixture layer consisting of Fe and overlay. These bearings were also subjected to the same tests as those explained in connection with Table 1.. In this case, the results also showed tendencies similar to those of the results shown in Table 1.

Fretting does not easily occur in the case of the testing bearings described above. For this reason, first and second bearings were actually mounted in an engine, the first bearing being the same as the bearing having the Sn-2%Cu-6%Sb overlay shown in Table 1 except that its rear face-plating layer was 0.5 microns thick, while the second bearing was the same as the first bearing except that its rear face-plating layer was 0.8 microns thick. That is, each of the first and second bearings was mounted in an inline type of 1,500-cc 4cylinder diesel engine provided with a turbocharger, and the occurrence or nonoccurrence of fretting was visually inspected. It was confirmed that no fretting occurred on the first bearing or the second bearing, but migration was observed on the second bearing through the visual inspection.

As described above, in accordance with the first 1 17 aspect of the present invention, there is provided a multi-layer type sliding bearing of aluminium alloy which has a mixture layer constituted by a mixture of the constituents of the overlay and one element selected from the group consisting of Ni, Co and Fe, the mixture layer being provided between the bearing layer of aluminium alloy and the overlay. Since this first multi-layer type sliding bearing of aluminium alloy is superior in maximum fatigue load:;and maximum seizure load in pomparison with the prior, art multilayer type sliding bearing of aluminium alloy, it is; free from the aforesaid disadvantages of the prior art.. Accordingly, the first multilayer type sliding bearinq of aluminium alloy is pa. rticularly suitable for use in It., a high- speed diesel engine or an engine with a

2,11 turbocharger which is used under high-speed and highload conditions.

The multi-layer type sliding bearing of aluminium alloy according to a preferred feature of the invention has a rear face-plating layer in addition to the construction of the first multi-layer type sliding bearing of aluminium alloy described above. The second multi-layer type sliding bearing of aluminium alloy is superior in maximum fatigue load and maximum seizure load to the prior art multi-layer type sliding bearings of aluminium alloy and has the ability to improve fretting. Accordingly, it is possible to eliminate the aforesaid disadvantages of the prior art., i 18

Claims

A multi-layer type sliding bearing of aluminium alloy having a backing layer of steel, a bearing layer of aluminium alloy bonded to the backing layer, an overlay, and a mixture layer of a thickness of not more than 0.5 pm between the bearing layer and the overlay in a bonded relation to both the bearing layer and the overlay, the mixture layer being. constituted by the mixture of the overlay and one element selected from the group consisting of Ni, Co and Fe, the overlay consisting by weight of 0 to 15% Cu, 0 to 20% Sb, and thd balance Sn and incidental Ir, impurities.
2. A bearing as claimed in Claim 1 in which the backing layer has, bonded to its side opposite to tl-i<-.it of the bearing layer, a rear faceplating layer.

21) 1 ()
3. A bearing as claimed in Claim 2 in which the rear face-plating layer consists of the same constituents as the overlay.
4. A bearing as claimed in Claim 2 or claim 3 in which the thickness of the rear face-plating layer is in the range of 0.1 to 5jum.
5. A bearing as claimed in any of Claims 1 to 4 in which the thickness of the mixture layer is 0.05 to 0. 3 pm.
6. A bearing as claimed in any of Claims I- to s P4 19 in which the overlay consists by weight of not more than 5%Cu, 0.5 to 10%Sb, and the balance Sn.
7. A method of producing a multi-layer type r? sliding bearing of aluminium alloy comprising providing a half cylindrical of cylindrical bearing member made of an aluminium alloy, the bearing member being bonded onto a backing layer of steel, electrolytically providing an overlay on the inner face of'the bearing 117 member which overlay consists by weight of 0 to 15% Cu, 0 to 20% Sb, and the balance Sn and incidental impurities, and providing a mixture layer having a thickness of not more than 5 yrn between the overlay and the bearing layer of altiminium alloy by a! combination of an electroless substitution method and an overlay electroplating method, the mixture layer being constituted by a mixture of the constituents of the overlay and one element selected from the group consisting of Ni, Co and Fe.

211
8. A method as claimed in Claim 7 in which the step of electrolytically providing the overlay on the inner face of the bearing member includes electrolytically providing, on the rear face of the bearing, a plating layer which has a thickness of 0.1 to Sym and which is constituted by constituents which are the same as those of the overlay.
9. A multi-layer type sliding bearing substantially as described herein, with reference to Figures 1, 2c and 2c-1 or as described herein with reference to Figure 3 of the accompanying drawings.

Published 1990a', The PatentOffice. State House, 66 71 High Holborn. London WCIR4TP. Further copies maybe obtainedfrom The Patent office. Sales Branch, St Mary Cray. Orpingtor., Kent BR5 3RD. Printed by MWtIpIeX teqhniques Itd. St Mary Cray. Kent. Con. 1 87